There are occasions where two members, namely, one made of an aluminum-based material and the other made of an iron-based material, need to be joined together. Such members are regarded to be difficult to bond together because the melting point of aluminum greatly differs from that of iron while an aluminum oxide film that covers the aluminum-based member is so hard that welding is difficult to perform.
To address the problem, it is known to apply friction stir bonding as disclosed, for example, in Japanese Patent Application Laid-Open Publication No. 2007-30043 (JP 2007-30043 A).
The friction stir bonding disclosed in JP 2007-30043 A will be described below with reference to FIGS. 5A to 5C hereof. FIG. 5B is a cross-sectional view taken along line b-b of FIG. 5A while FIG. 5C is a cross-sectional view taken along line c-c of FIG. 5A.
As shown in FIG. 5A, an adhesive 102 is applied onto a flat plate 101, on which an angled member 103 is placed. Friction stir bonding is used to melt and bond the angled member 103 with the flat plate 101 to form a bonded structure 104.
The principle of friction stir bonding is described as follows: when a spindle rotating at a high speed is pressed against the angled member 103, the frictional heat generated by the rotation melts part of the angled member 103 and the flat plate 101. The melted portion moves as the spindle is moved along the angled member 103, and solidifies as the spindle moves away.
As shown in FIG. 5B, a welded portion 106 is formed, which serves to join the flat plate 101 with the angled member 103. The adhesive 102 is not particularly heat-resistant, and accordingly burns away on being subjected to the frictional heat in the vicinity of the welded portion 106.
As shown in FIG. 5C, a recess 107, referred to as a stop mark, is left at an end of the welded portion 106. The recess 107 is created when the spindle is withdrawn.
Cases shall be considered hereunder in regard to the friction stir bonding described above being applied to production of a door and a hood skin of a vehicle and other lid-shaped objects.
FIGS. 6A and 6B are descriptive views showing friction stir bonding being used to produce a lid-shaped object.
As shown in FIG. 6A, an adhesive is applied onto a first member 111 made of an aluminum-based material to form adhesive layers 112, 112, on which a second member 113 made of an iron-based material is overlaid. The edge of the first member 111 is then bent over the second member 113, as indicated by the arrow.
As shown in FIG. 6B, friction stir bonding is then used to create a welded portion 114 so as to bond the first member 111 with the second member 113. The bond formed using the adhesive 112 and the bond formed using the welded portion 114 can firmly join the second member 113 with the first member 111.
As shown in FIG. 6A, the adhesive layers 112, 112 are desirably applied in a non-continuous manner to avoid being affected by the frictional heat. However, non-continuous application is a more cumbersome task than continuous application and takes a longer period of time, resulting in an increased adhesive application cost.
Further, as shown in FIG. 6B, since a recess 115, referred to as a stop mark, is inevitably left, the recess 115 must be filled with a putty or other materials. Specifically, an extra step of filling the stop mark must be added, resulting in an increased cost of producing a lid-shaped object.